For many years, it has been known that oxygenation results in the biological and chemical breakdown of organic contaminants in effluent or wastewater. The surface of a body of liquid provides some oxygen uptake or absorption, because of its exposure to the atmosphere. However, when prior art diffused gas systems are used in order to accelerate the oxygenation, they require the use of additional devices to promote proper mixing. It is well-known to be important for cost reasons, to Ionize the time and energy required for such treatment. The unique design of the diffuser of this invention enables it to efficiently achieve both of these requirements from a single power source.
Similar considerations apply to the newer area of commerce, often referred to as aquaculture or "fish farming". The medium in which fish will thrive must be rich in oxygen and well mixed. Supplying adequate amounts of oxygen, and dispersing it uniformly throughout the tank is of primary importance to the success of such enterprises. The diffuser of this invention accomplishes both functions economically.
In the treatment of effluent, there have been a number of methods used in the prior art to expose a greater surface area of effluent for contact with the atmosphere, including devices such as fountains to spray the liquid into the air. Others, such as the Bearden patent, U.S. Pat. No. 3,852,384 have devised submerged vertical columns with means to intermix liquid and air passing therethrough. Kober, U.S. Pat. No. 3,133,878 discloses an arrangement to create a circular flow of the liquid and treating gas. Like many others, both of these patents employ a perforated pipe to dispense the gas.
The Morgan patent, U.S. Pat. No. 3,232,866 is of interest because it relates to the spacing of diffusers in the container of liquid being treated. Morgan discloses a critical relationship between oxygen uptake and the arrangement of the diffuser heads. The Goudy et. al. patent, U.S. Pat. No. 4,597,530 discusses several prior art patents in the field and covers a diffuser in the shape of a disc which is designed in such a manner as to prevent dogging of its orifices.
Some prior art employs coarse aerators or "spargers" which have the advantage of moving the liquid upward, or rolling it, as a result of relatively large bubbles of air boiling to the surface. Current diffusers which produce fine bubbles, on the other hand, are less effective in mixing or rolling the liquid as the bubbles rise to the surface, but are more effective than the coarse diffusers in their aeration effectiveness, because of the greater surface area of the fine bubbles exposed to the liquid. The design of the present invention is effective both in mixing and aeration.
Some diffusers of the prior art employ a membrane through which air is passed to produce fine bubbles, while others employ a porous stone. They are of a simpler construction than that of the present invention, and like conventional coarse air diffusers, they merely inject air into the liquid which forms large bubbles without enhancing oxygenation. The membranes of the prior art, however, are so flexible and not self supporting, that they require mounting on a kind of mandrel or internal support. Moreover, they are so easily distended when subjected to air pressure, that air is not emitted from their entire circumference. For example a tubular shaped diffuser emits air mostly from its upper surface.